This mix of Mexican and Japanese flavors—seared steak marinated in a rich, sweet sauce and wrapped in a taco—makes a really quick meaty feast. Normally, meat is marinated before cooking, but here you cook the steak and then let it cool in the marinade to absorb all that flavor. The steaks can be left to marinate for up to four days—the longer the better.
First prepare the marinade. Mix the miso paste, mirin, sugar, and olive oil, stirring well to dissolve the sugar. Season with salt and pepper and add a tablespoon of water if the mixture needs loosening a little.
Leave the fat on the steaks to keep them from drying out as you cook them. Season them well with salt and pepper and sear in a hot oiled frying pan for 2–3 minutes on each side for rare/medium-rare, or until cooked to your liking. (Shake the pan gently as you put the steaks in the pan to keep them from sticking, otherwise they might burn.) Render the fat by tipping the steaks onto their sides and cooking until the fat is golden and crisp. Keep basting the steaks as you cook.
When the steaks are cooked, remove from the pan and cut off the remaining layer of fat. Place the steaks in the marinade, coating all sides. Leave to rest, spooning the marinade over now and again.
Meanwhile, prepare the quick pickled cabbage. Put the cabbage in a bowl and season with salt and pepper. Add the rice vinegar, sesame oil, and chile flakes. Toss the mixture to coat, then leave to soften slightly for a couple of minutes.
Meanwhile, mix together the wasabi and mayonnaise, taste, and add a little more wasabi if you like a stronger flavor.
Heat the tortillas for 30–60 seconds over a naked gas flame until charred and lightly toasted (use a pan if you don’t have gas). Roll them around a rolling pin while they’re still hot, and hold until cooled to set in half-moon taco shapes.
Drain the beef of any excess marinade, then slice and place in the tacos. Top with the cabbage (drained of excess liquid) and a little wasabi mayo.